In the fabrication process for semiconductor devices, numerous processing steps must be performed on a semi-conducting substrate to form various circuits. The process may consists of as many as several hundred processing steps. Each processing step is executed in a process chamber such as an etcher, a physical vapor deposition (PVD) chamber, a chemical vapor deposition (CVD) chamber or an ion implanter.
In the vast majority of the processing steps, a special environment of either a high vacuum, a low vacuum or a gas plasma environment must be provided for the process. For instance, in a PVD (or sputter) chamber, a high vacuum environment must be provided to surround the wafer such that particles sputtered from a metal target can travel to and be deposited on an exposed surface of the wafer. In other process chambers, such as in a plasma enhanced chemical vapor deposition (PECVD) chamber, a plasma cloud of a reactant gas or gases is first formed in vacuum over a wafer such that the deposition of a chemical substance can occur on the surface of the wafer. During any processing step, the wafer must also be kept in an extremely clean environment without the danger of being contaminated. The processing of a wafer is therefore conducted in a hermetically sealed environment that is under vacuum and completely isolated from the atmosphere. Numerous vacuum process chambers have been provided for such purpose.
A typical vacuum process chamber 10 consists of a horizontal furnace tube 12 and a cantilever loader assembly 14 is shown in FIG. 1. The vacuum process chamber 10 is a low pressure chemical vapor deposition chamber that is frequently used for depositing films on wafers. The furnace tube 12 is formed in an elongated shape with one end 16 sealed and connected to an evacuation means (not shown) such as a high capacity vacuum pump. The furnace tube 12 can be fabricated of a high temperature material such as quartz and be equipped with a flange 18 for sealing against a door 20 mounted on a cantilever loader assembly 14. The cantilever loader assembly 14 is typically provided with cantilever sheaths 22 for supporting a plurality of wafer boats (not shown). Wafers 24, which are positioned on wafer boats are loaded onto the cantilever sheaths 22.
In operating the vacuum process chamber 10, a cantilever loader assembly 14 is first loaded with wafers 24 which are positioned in various wafer boats (not shown) on the cantilever sheaths. The cantilever loader assembly is then slid into the furnace tube 12 on a loader stage (not shown) and guided into the furnace tube 12. After the loader assembly 14 is completely inserted into the furnace tube 12, the door 20 on the cantilever loader assembly 14 engages the flange 18 on the furnace tube 12 and is pressed tightly against an O-ring seal (not shown) on the flange 18. In order to ensure that the door 20 is properly closed on the furnace tube 12, a pressure switch 26 is provided in the flange 18 for sensing the proper positioning of the door 20. The pressure switch 26 may either be pressed down by the door 20 itself, or by a pressure switch push pin 28 which is mounted on the door 20 for engaging the pressure switch 26 when the door 20 is properly closed on flange 18. A signal is sent out by the pressure switch 26 after a proper engagement has been achieved to a central process controller which then starts the high capacity vacuum pump for evacuating the interior cavity 30 of the furnace tube 12.
A detailed side view of the cantilever loader assembly 14 which illustrates a loader stage 34 for supporting the door 20 is shown in FIG. 2. The loader stage 34 has three sheaths 36 mounted thereto at end 38. A loader bracket 40 is utilized for mounting the door 20 to the loader stage 34 through a mounting block 42. The mounting block 42 is fastened to the loader bracket 40 through an aperture 44 and a bolt 46 and spring 48. The boat 46 is fastened to threads provided in an aperture 50 in the loader bracket 40. The loader bracket 40 is fastened to the loader stage 34 through mechanical fastening means 52. After the mounting block 42 is fastened to the loader bracket 40, the door 20 is connected to the loader stage 34 by inserting an universal joint 54 for guiding into the aperture 56 of the mounting block 42 and then fastening by screw 60 and spring 58. During the assembly of the door 20 to the loader stage 34, the three sheaths 36 are mounted through sheath bellows 62 that are provided on the door 20. A plane view of the door 20 is also shown in FIG. 2 illustrating the pressure switch push pin 28, the sheaths 36 and the universal joint 54.
As shown in FIG. 2, the universal joint 54 mounted on the door 20 is used to facilitate the mounting of the door 20 on the mounting block 42. The universal joint 54 allows an easy alignment through the mounting hole 56 located in the mounting block 42 such that it can be guided through the hole for fastening by bolt 60. In this conventional set up for a low pressure chemical vapor deposition chamber, the insertion of the universal joint 54 through the mounting hole 56 is sometimes difficult to carry out due to the frictional force existed between the universal joint and the hole. The friction between the two members limits the freedom of movement of the universal joint 54 and affects the mounting of the door 20 to the mounting block 42.
In the conventional set up, shown in FIG. 2, the pressure switch push pin 28 is used to sense and determine the proper positioning or sealing of the door 20 on the mounting flange 18 located on the furnace tube 12 (shown in FIG. 1). The mechanical force required to push the pressure switch push pin 28 against the pressure switch 26 sometimes cause the tilting of the door 20 and thus preventing a perfect flush mounting of the two members together. A defectively mounted position occurs when a seal between the door and the flange is not achieved, even though the pressure switch 26 already sent out a signal to the central process controller indicating that a seal has been achieved and thus the vacuum pump is turned on. Such defective conditions therefore result in a poorly sealed chamber and on inability of the cavity in the furnace tube to achieve a desirable vacuum.
It is therefore an object of the present invention to provide an apparatus for hermetically sealing a vacuum process chamber that does not have the drawbacks and shortcomings of the conventional apparatus.
It is another object of the present invention to provide an apparatus for hermetically sealing a vacuum process chamber that has minimum frictional engagement between two members sealed against each other.
It is a further object of the present invention to provide an apparatus for hermetically sealing a vacuum process chamber that utilizes a sensing device for sensing the state of sealing between two components without requiring mechanical contact.
It is another further object of the present invention to provide an apparatus for hermetically sealing a vacuum process chamber by utilizing a ball bearing between two mating members such that frictional engagement is minimized.
It is still another object of the present invention to provide an apparatus for hermetically sealing a vacuum process chamber by utilizing a photosensing device for detecting a state of engagement between two members.
It is yet another object of the present invention to provide an apparatus for hermetically sealing a vacuum process chamber that utilizes a flag traversing on a moving component and a photo transmitter/receiver that is stationarily mounted on a second component for detecting the state of engagement between the two components.
It is still another further object of the present invention to provide a method for hermetically sealing a vacuum process chamber by utilizing a ball bearing for engagement between the members to reduce frictional force.
It is yet another farther object of the present invention to provide a method for hermetically sealing a vacuum process chamber by utilizing a photosensing device such that mechanical contact between two sealing members is completely eliminated.